The present invention relates in general to vertical broaching machines and, more particularly, to a vertical broaching machine having a single broach.
When machining keyways for cylindrical objects such as hubs or couplings, it is necessary to have the broach pass through the center of the work piece. Then, either the broach is moved to remove metal from the work piece or the broach is held stationary and the work piece is moved with respect to the broach. Broaching machines of this type generally have the broach holder positioned above the work piece and a broach pulling unit below the work piece which grabs the bottom of the broach and causes the vertical movement of the broach by means of a mechanized pulling unit.
One example of a vertical broaching machine which does not use a pulling unit is illustrated in U.S. Pat. No. 4,266,894. In this device, the broach passes through the center of the blank to be machined and performs the cutting operation. The broach is then withdrawn back through the machined work piece and a new work piece is then inserted into the proper location to perform the same operation. All of the guides which are utilized to maintain the broach in a vertical relationship with respect to the bore of the work piece are positioned above the work piece. It would be advantageous if guides could be positioned below the work piece to maintain the broach and mandrel in a perfectly vertical orientation. However, this is not provided for in the '894 patent.
Another vertical broaching machine is illustrated in U.S. Pat. No. 5,184,985. This broaching machine illustrates a machine having multiple broaches held in a broach head. The broaches are utilized to machine holes in a plate for steam generators. The broach holder and broach pulling unit are both placed on a slide mechanism which provides for the movement of the broach head and pulling unit along a horizontal axis. In addition, the work piece can be moved along a horizontal axis which is perpendicular to the movement of the broach head. This mechanism is extremely complicated and expensive in order to accurately control the movement of the broach holder and pulling unit with respect to the work piece. Although this machine is particularly well adapted for machining multiple holes in a large work piece, it is not particularly well adapted for machining a single keyway in an individual work piece. The reason is that it would be cost prohibitive to use such a sophisticated device to machine individual keyways in singular work pieces. Furthermore, there is no provision to accurately maintain and guide the broach in a vertical position while cutting the metal.
Another patent is U.S. Pat. No. 5,183,374 which illustrates a horizontal broach mounted on a standard which itself moves along a horizontal axis. The broach also can move up and down along a vertical axis. In the '374 patent, the tool itself moves but the work piece does not. The broach itself is not supported at both ends to maintain it in alignment during the broaching operation.
A problem with all of the prior art devices is that they do not provide a relatively inexpensive vertical broaching machine which can cut various depth keyways in cylindrical piece parts. Furthermore, none of the other prior art devices provide a vertical broaching machine which provides improved means for maintaining the broach in vertical alignment during the broaching operation.
The broaching machine of the present invention provides a vertical broach which passes through the bore of a piece part to be machined. There is a stationary bed plate upon which is positioned a moveable vise. The vise grips the piece part to be machined. The movement of the vise is accurately controlled by means of a solid state control system. There are upper and lower broach guide means which are disposed above and below the piece part. The broach guide means closely receive the broach during the machining operation. These maintain the broach in vertical alignment with the center bore of the piece part and increase the precision of the material removal during the broaching operation. The piece part is moved away from engagement with the broach teeth each time the broach is raised vertically and back into engagement with the teeth each time the broach is lowered and pulled in its cutting cycle. The piece part is moved out of engagement with the broach upon completion of the broaching operation such that the teeth of the broach do not engage the work piece which may result in inadvertent removal of additional material causing the machined area to be out of tolerance.